Yes, the rice should be cooked first.
How much would depend on how much rice you want in it. The only other sausage that I'm familiar with that includes rice is Cajun Boudin. A quick check of one of my Boudin recipes calls for 4 lbs of meat and 3 cups of uncooked rice (measure, then cook). Another recipe (in chef Donald Link's book) calls for 2.5 lbs of meat to 7 cups of cooked rice. I haven't made this recipe, but the picture looked like it had a lot of rice in it.
I'd think the blandness of the rice would make the sausage really taste mild, so unless that's what you are looking for I would expect you'd have to up the seasonings quite a bit. You'll have to experiment with it until you're happy.
I'd also expect for the sausage/rice mixture to be pretty dry, so you'll probably have to add adequate liquid to get it will mix well. You'll also want to make sure that the fat ratio is high enough to compensate for the rice. Otherwise, I think it will be crumbly when cooked.